Most surgical and nonsurgical treatments of painful temporomandibular joint internal derangements are primarily directed toward relief of pain and dysfunction; correction of disc displacement is increasingly of lesser or no concern. However, internal derangements are variably progressive and, in some patients, cause condylar deformity with secondary deficiency of the mandible. If data support the hypothesis that condylar deformity and growth retardation can result from a displaced disc, and, conversely, that a normally positioned disc permits normal growth and maintains condylar mass, a goal of any treatment for reducing disc displacement should include reestablishment of a normal disc/condyle relationship. Functional appliance therapy for the deficient mandible may be most effective in those patients that present with a normal disc/condyle relationship; if a reducing disc is present, such therapy may be most effective only when the appliance advances the condyle to a position beneath the disc.